The ad included a clip of Cheney on MSNBC in 2009 saying she opposes a constitutional ban on same-sex marriage and supports the State Department extending benefits to same-sex couples.

"MSNBC, the go-to network for Barack Obama and Washington's liberal elites. So what's Liz Cheney doing here?" The voiceover in the new ad, created by American Principles Fund, said. "In Wyoming Cheney campaigns as a conservative, in Washington she appears on MSNBC to campaign against the marriage amendment and support government benefits for gay couples."

"I applaud, for example, the State Department decision to extend benefits for same-sex couples around the world," Cheney said in the ad.

"Liz Cheney: Wrong for Wyoming," the ad concluded.

The ad is the latest attack Cheney has had to field in the Wyoming Senate race on same-sex marriage. In late August, Cheney's campaign released a statement saying she does not support same-sex marriage even though her sister, Mary Cheney, is openly lesbian. That statement was in response to a "push poll" asking whether Wyoming voters were aware that Cheney "supports abortion and aggressively promotes gay marriage."